Genetic analysis of the gene cluster encoding nonfimbrial adhesin I from an Escherichia coli uropathogen

Pili Assembled by the Chaperone/Usher Pathway in Escherichia coli and Salmonella

Gram-negative bacteria assemble a variety of surface structures, including the hair-like organelles known as pili or fimbriae. Pili typically function in adhesion and mediate interactions with various surfaces, with other bacteria, and with other types of cells such as host cells. The chaperone/usher (CU) pathway assembles a widespread class of adhesive and virulence-associated pili. Pilus biogenesis by the CU pathway requires a dedicated periplasmic chaperone and integral outer membrane protein termed the usher, which forms a multifunctional assembly and secretion platform. This review addresses the molecular and biochemical aspects of the CU pathway in detail, focusing on the type 1 and P pili expressed by uropathogenic Escherichia coli as model systems. We provide an overview of representative CU pili expressed by E. coli and Salmonella, and conclude with a discussion of potential approaches to develop antivirulence therapeutics that interfere with pilus assembly or function.

Pathogenesis of human diffusely adhering Escherichia coli expressing Afa/Dr adhesins (Afa/Dr DAEC): current insights and future challenges

The pathogenicity and clinical pertinence of diffusely adhering Escherichia coli expressing the Afa/Dr adhesins (Afa/Dr DAEC) in urinary tract infections (UTIs) and pregnancy complications are well established. In contrast, the implication of intestinal Afa/Dr DAEC in diarrhea is still under debate. These strains are age dependently involved in diarrhea in children, are apparently not involved in diarrhea in adults, and can also be asymptomatic intestinal microbiota strains in children and adult. This comprehensive review analyzes the epidemiology and diagnosis and highlights recent progress which has improved the understanding of Afa/Dr DAEC pathogenesis. Here, I summarize the roles of Afa/Dr DAEC virulence factors, including Afa/Dr adhesins, flagella, Sat toxin, and pks island products, in the development of specific mechanisms of pathogenicity. In intestinal epithelial polarized cells, the Afa/Dr adhesins trigger cell membrane receptor clustering and activation of the linked cell signaling pathways, promote structural and functional cell lesions and injuries in intestinal barrier, induce proinflammatory responses, create angiogenesis, instigate epithelial-mesenchymal transition-like events, and lead to pks-dependent DNA damage. UTI-associated Afa/Dr DAEC strains, following adhesin-membrane receptor cell interactions and activation of associated lipid raft-dependent cell signaling pathways, internalize in a microtubule-dependent manner within urinary tract epithelial cells, develop a particular intracellular lifestyle, and trigger a toxin-dependent cell detachment. In response to Afa/Dr DAEC infection, the host epithelial cells generate antibacterial defense responses. Finally, I discuss a hypothetical role of intestinal Afa/Dr DAEC strains that can act as "silent pathogens" with the capacity to emerge as "pathobionts" for the development of inflammatory bowel disease and intestinal carcinogenesis.

Role of Flagella in Adhesion of Escherichia coli to Abiotic Surfaces

Understanding the interfacial activity of bacteria is of critical importance due to the huge economic and public health implications associated with surface fouling and biofilm formation. The complexity of the process and difficulties of predicting microbial adhesion to novel materials demand study of the properties of specific bacterial surface features and their potential contribution to surface attachment. Here, we examine flagella, cell appendages primarily studied for their cell motility function, to elucidate their potential role in the surface adhesion of Escherichia coli-a model organism and potential pathogen. We use self-assembled monolayers (SAMs) of thiol-bearing molecules on gold films to generate surfaces of varying hydrophobicity, and measure adhesion of purified flagella using quartz crystal microbalance. We show that flagella adhere more extensively and bind more tightly to hydrophobic SAMs than to hydrophilic ones, and we propose a two-step vs a single-step adhesion mechanism that accounts for the observed dissipation and frequency changes for the two types of surfaces, respectively. Subsequently, study of the adhesion of wild-type and flagella knockout cells confirms that flagella improve adhesion to hydrophobic substrates, whereas cells lacking flagella do not show preferred affinity to hydrophobic substrates. Together, these properties bring about an interesting ability of cells with flagella to stabilize emulsions of aqueous culture and dodecane, not observed for cells lacking flagella. This work contributes to our overall understanding of nonspecific bacterial adhesion and confirms that flagella, beyond motility, may play an important role in surface adhesion.

Adhesive organelles of Gram-negative pathogens assembled with the classical chaperone/usher machinery: structure and function from a clinical standpoint

This review summarizes current knowledge on the structure, function, assembly and biomedical applications of the superfamily of adhesive fimbrial organelles exposed on the surface of Gram-negative pathogens with the classical chaperone/usher machinery. High-resolution three-dimensional (3D) structure studies of the minifibers assembling with the FGL (having a long F1-G1 loop) and FGS (having a short F1-G1 loop) chaperones show that they exploit the same principle of donor-strand complementation for polymerization of subunits. The 3D structure of adhesive subunits bound to host-cell receptors and the final architecture of adhesive fimbrial organelles reveal two functional families of the organelles, respectively, possessing polyadhesive and monoadhesive binding. The FGL and FGS chaperone-assembled polyadhesins are encoded exclusively by the gene clusters of the γ3- and κ-monophyletic groups, respectively, while gene clusters belonging to the γ1-, γ2-, γ4-, and π-fimbrial clades exclusively encode FGS chaperone-assembled monoadhesins. Novel approaches are suggested for a rational design of antimicrobials inhibiting the organelle assembly or inhibiting their binding to host-cell receptors. Vaccines are currently under development based on the recombinant subunits of adhesins.

Structural analysis of the Saf pilus by electron microscopy and image processing

Bacterial pili are important virulence factors involved in host cell attachment and/or biofilm formation, key steps in establishing and maintaining successful infection. Here we studied Salmonella atypical fimbriae (or Saf pili), formed by the conserved chaperone/usher pathway. In contrast to the well-established quaternary structure of typical/FGS-chaperone assembled, rod-shaped, chaperone/usher pili, little is known about the supramolecular organisation in atypical/FGL-chaperone assembled fimbriae. In our study, we have used negative stain electron microscopy and single-particle image analysis to determine the three-dimensional structure of the Salmonella typhimurium Saf pilus. Our results show atypical/FGL-chaperone assembled fimbriae are composed of highly flexible linear multi-subunit fibres that are formed by globular subunits connected to each other by short links giving a "beads on a string"-like appearance. Quantitative fitting of the atomic structure of the SafA pilus subunit into the electron density maps, in combination with linker modelling and energy minimisation, has enabled analysis of subunit arrangement and intersubunit interactions in the Saf pilus. Short intersubunit linker regions provide the molecular basis for flexibility of the Saf pilus by acting as molecular hinges allowing a large range of movement between consecutive subunits in the fibre.

Evolution of the chaperone/usher assembly pathway: fimbrial classification goes Greek

Many Proteobacteria use the chaperone/usher pathway to assemble proteinaceous filaments on the bacterial surface. These filaments can curl into fimbrial or nonfimbrial surface structures (e.g., a capsule or spore coat). This article reviews the phylogeny of operons belonging to the chaperone/usher assembly class to explore the utility of establishing a scheme for subdividing them into clades of phylogenetically related gene clusters. Based on usher amino acid sequence comparisons, our analysis shows that the chaperone/usher assembly class is subdivided into six major phylogenetic clades, which we have termed alpha-, beta-, gamma-, kappa-, pi-, and sigma-fimbriae. Members of each clade share related operon structures and encode fimbrial subunits with similar protein domains. The proposed classification system offers a simple and convenient method for assigning newly discovered chaperone/usher systems to one of the six major phylogenetic groups.

FGL chaperone-assembled fimbrial polyadhesins: anti-immune armament of Gram-negative bacterial pathogens

This review summarizes the current knowledge on the structure, function, assembly, and biomedical applications of the family of adhesive fimbrial organelles assembled on the surface of Gram-negative pathogens via the FGL chaperone/usher pathway. Recent studies revealed the unique structural and functional properties of these organelles, distinguishing them from a related family, FGS chaperone-assembled adhesive pili. The FGL chaperone-assembled organelles consist of linear polymers of one or two types of protein subunits, each possessing one or two independent adhesive sites specific to different host cell receptors. This structural organization enables these fimbrial organelles to function as polyadhesins. Fimbrial polyadhesins may ensure polyvalent fastening of bacteria to the host cells, aggregating their receptors and triggering subversive signals that allow pathogens to evade immune defense. The FGL chaperone-assembled fimbrial polyadhesins are attractive targets for vaccine and drug design.

Diffusely adherent Escherichia coli strains expressing Afa/Dr adhesins (Afa/Dr DAEC): hitherto unrecognized pathogens

Diffusely adherent Escherichia coli (DAEC) strains are currently considered to constitute a putative sixth group of diarrheagenic E. coli. However, on the basis of their diffuse adherence to HEp-2 and HeLa cells, the detection of afa/dra/daa-related operons encoding this adherence phenotype, and the mobilization of decay-accelerating factor, both commensal and pathogenic strains can be classified as Afa/Dr DAEC isolates. Furthermore, strains associated with diarrheal diseases and strains causing extra-intestinal infections can also be identified as Afa/Dr DAEC strains. Although several cell signaling events that occur after epithelial cells have been infected by Afa/Dr DAEC have been reported, the pathophysiological processes that allow intestinal and extra-intestinal infections to develop are not fully understood. This review focuses on the genetic organization of the afa/dra/daa-related operons and on the virulence factors that trigger cellular responses, some of which are deleterious for the host cells. Finally, this review suggests future lines of research that could help to elucidate these questions.

The secreted autotransporter toxin, Sat, functions as a virulence factor in Afa/Dr diffusely adhering Escherichia coli by promoting lesions in tight junction of polarized epithelial cells

Afa/Dr diffusely adhering Escherichia coli (DAEC) strains are responsible for urinary tract and intestinal infections. Both in intestine and kidney, the epithelial cells forming epithelium are sealed by junctional domains. We provide evidence that the Secreted autotransporter toxin, Sat, belonging to the subfamily of serine protease autotransporters of Enterobacteriaceae (SPATEs), acts as a virulence factor in Afa/Dr DAEC by promoting lesions in the tight junctions (TJs) of polarized epithelial Caco-2/TC7 cells. Southern blot analysis reveals that the prototype strains of the subclass-1 and subclass-2 typical Afa/Dr DAEC strains, hybridize with a sat probe. Using the wild-type IH11128 strain, the recombinant E. coli AAEC185 strain that expresses Sat, the recombinant E. coli that expresses both Dr adhesin and Sat, we report that Sat in monolayers of cultured enterocyte-like Caco-2/TC7 cells, induces rearrangements of the TJs-associated proteins ZO-1, ZO-3 and occludin, and increases the formation of domes as the result of an increase in the paracellular permeability without affecting the transepithelial electrical resistance of the cell monolayers. Moreover, we observe that Sat-induced disassembly of TJs-associated proteins is dependent on the serine protease motif. Finally, an analysis of the prevalence of the sat gene in three collections of Afa/Dr DAEC strains collected from the stools of children with and without diarrhoea, and from the urine of patients with urinary tract infection (UTI) shows that: (i) the sat gene is highly prevalent in UTI-associated Afa/Dr DAEC strains (88% positive), (ii) the sat gene is generally absent from Afa/Dr DAEC strains collected from the stools of children without diarrhoea (16% positive); whereas (iii) it is present in about half of the strains collected from the stools of children with diarrhoea (46% positive).

Adhesins and invasins of pathogenic Escherichia coli

Pathogenic E. coli cause both intestinal and extra-intestinal infections in humans and animals. Bacteria must be able to adhere to host cells if they are to colonize and to invade their hosts. Numerous E. coli adhesins with different morphological features and receptor specificities have been identified. Many bacteria produce several adhesins with different receptor specificities. Although not all adhesin receptors have been identified yet, it appears that adhesins generally behave as lectins, recognizing oligosaccharide residues of glycoproteins or glycolipids. This review summarizes recent advances concerning host tissue colonization properties, providing new insights into adhesive organelle biogenesis in pathogenic E. coli and into the development of reservoirs of pathogenic bacteria in the host. To limit the length of this review, I will use examples of structural characteristics and invasive properties of a few bacterial adherence factors: type 1 pili, Afa adhesive sheath and some outer membrane adhesins.

Pathogenesis of Afa/Dr diffusely adhering Escherichia coli

Over the last few years, dramatic increases in our knowledge about diffusely adhering Escherichia coli (DAEC) pathogenesis have taken place. The typical class of DAEC includes E. coli strains harboring AfaE-I, AfaE-II, AfaE-III, AfaE-V, Dr, Dr-II, F1845, and NFA-I adhesins (Afa/Dr DAEC); these strains (i) have an identical genetic organization and (ii) allow binding to human decay-accelerating factor (DAF) (Afa/Dr(DAF) subclass) or carcinoembryonic antigen (CEA) (Afa/Dr(CEA) subclass). The atypical class of DAEC includes two subclasses of strains; the atypical subclass 1 includes E. coli strains that express AfaE-VII, AfaE-VIII, AAF-I, AAF-II, and AAF-III adhesins, which (i) have an identical genetic organization and (ii) do not bind to human DAF, and the atypical subclass 2 includes E. coli strains that harbor Afa/Dr adhesins or others adhesins promoting diffuse adhesion, together with pathogenicity islands such as the LEE pathogenicity island (DA-EPEC). In this review, the focus is on Afa/Dr DAEC strains that have been found to be associated with urinary tract infections and with enteric infection. The review aims to provide a broad overview and update of the virulence aspects of these intriguing pathogens. Epidemiological studies, diagnostic techniques, characteristic molecular features of Afa/Dr operons, and the respective role of Afa/Dr adhesins and invasins in pathogenesis are described. Following the recognition of membrane-bound receptors, including type IV collagen, DAF, CEACAM1, CEA, and CEACAM6, by Afa/Dr adhesins, activation of signal transduction pathways leads to structural and functional injuries at brush border and junctional domains and to proinflammatory responses in polarized intestinal cells. In addition, uropathogenic Afa/Dr DAEC strains, following recognition of beta(1) integrin as a receptor, enter epithelial cells by a zipper-like, raft- and microtubule-dependent mechanism. Finally, the presence of other, unknown virulence factors and the way that an Afa/Dr DAEC strain emerges from the human intestinal microbiota as a "silent pathogen" are discussed.

afa-8 Gene cluster is carried by a pathogenicity island inserted into the tRNA(Phe) of human and bovine pathogenic Escherichia coli isolates

We recently described a new afimbrial adhesin, AfaE-VIII, produced by animal strains associated with diarrhea and septicemia and by human isolates associated with extraintestinal infections. Here, we report that the afa-8 operon, encoding AfaE-VIII adhesin, from the human blood isolate Escherichia coli AL862 is carried by a 61-kb genomic region with characteristics typical of a pathogenicity island (PAI), including a size larger than 10 kb, the presence of an integrase-encoding gene, the insertion into a tRNA locus (pheR), and the presence of a small direct repeat at each extremity. Moreover, the G+C content of the afa-8 operon (46.4%) is lower than that of the E. coli K-12/MG1655 chromosome (50.8%). Within this PAI, designated PAI I(AL862), we identified open reading frames able to code for products similar to proteins involved in sugar utilization. Four probes spanning these sequences hybridized with 74.3% of pathogenic afa-8-positive E. coli strains isolated from humans and animals, 25% of human pathogenic afa-8-negative E. coli strains, and only 8% of fecal strains (P = 0.05), indicating that these sequences are strongly associated with the afa-8 operon and that this genetic association may define a PAI widely distributed among human and animal afa-8-positive strains. One of the distinctive features of this study is that E. coli AL862 also carries another afa-8-containing PAI (PAI II(AL862)), which appeared to be similar in size and genetic organization to PAI I(AL862) and was inserted into the pheV gene. We investigated the insertion sites of afa-8-containing PAI in human and bovine pathogenic E. coli strains and found that this PAI preferentially inserted into the pheV gene.

Pyelonephritogenic diffusely adhering Escherichia coli EC7372 harboring Dr-II adhesin carries classical uropathogenic virulence genes and promotes cell lysis and apoptosis in polarized epithelial caco-2/TC7 cells

Diffusely adhering Escherichia coli (DAEC) strains expressing adhesins of the Afa/Dr family bind to epithelial cells in a diffuse adherence pattern by recognizing a common receptor, the decay-accelerating factor (CD55). Recently, a novel CD55-binding adhesin, named Dr-II, was identified from the pyelonephritogenic strain EC7372. In this report, we show that despite the low level of sequence identity between Dr-II and other members of the Afa/Dr family, EC7372 induces pathophysiological effects similar to those induced by other Afa/Dr DAEC strains on the polarized epithelial cell line Caco-2/TC7. Specifically, the Dr-II adhesin was sufficient to promote CD55 and CD66e clustering around adhering bacteria and apical cytoskeleton rearrangements. Unlike other Afa/Dr DAEC strains, EC7372 expresses a functional hemolysin that promotes a rapid cellular lysis. In addition, cell death by apoptosis or necrosis was observed in EC7372-infected Caco-2/TC7 cells, depending on infection time. Our results indicate that EC7372 harbors a pathogenicity island (PAI) similar to the one described for the pyelonephritogenic strain CFT073, which carries both hly and pap operons. Cumulatively, our findings indicate that strain EC7372 can be considered a prototype of a subclass of Afa/Dr DAEC isolates that have acquired a PAI harboring several classical uropathogenic virulence genes.

The afa-related gene cluster in necrotoxigenic and other Escherichia coli from animals belongs to the afa-8 variant

Six hundred and nine necrotoxigenic Escherichia coli type 1 and 2 (NTEC1 and NTEC2) and non-NTEC isolated in Western and Southern Europe, North Africa and Canada from diseased calves, pigs, humans, poultry, and 55 isolated from asymptomatic calves were studied for the identification of afa-related sequences to the recently described afa-7 and afa-8 gene cluster variants from two bovine Escherichia coli (Lalioui et al., 1999). Colony hybridization and PCR assays for the afaD-7, afaE-7, afaD-8 and afaE-8 identified the afa-related sequences to the afa-8 gene cluster in most (67/79; 85%) of the E. coli positive with the Afa-f family probe and in 14 additional strains negative with the Afa-f probe. No E. coli was positive for the afa-7 gene cluster. The existence of afa-8 positive strains was thus confirmed among bovine E. coli and for the first time among porcine, poultry and human E. coli. Sequencing of the afaE-8 amplicon of nine strains from the different host species showed a high degree of conservation (>95% at the DNA level; >92% at the amino-acid level). The afa-8 gene cluster was more frequent in E. coli from diseased calves (18%) than from piglets (12%), humans (6%) and poultry (5%). Bovine NTEC2 (26%) were more frequently positive than NTEC 1 (20%) and non-NTEC (11%). E. coli isolated from asymptomatic calves were rarely positive: one NTEC2 (3%) and no non-NTEC. The afa-8 gene cluster was located on the Vir plasmid in 11/23 NTEC2, but no plasmid localization was detected in NTEC1 or non-NTEC.

Pilus biogenesis via the chaperone/usher pathway: an integration of structure and function

The molecular basis of how pathogenic bacteria cause disease has been studied by blending a well-developed genetic system with X-ray crystallography, protein chemistry, high resolution electron microscopy, and cell biology. Microbial attachment to host tissues is one of the key events in the early stages of most bacterial infections. Attachment is typically mediated by adhesins that are assembled into hair-like fibers called pili on bacterial surfaces. This article focuses on the structure-function correlates of P pili, which are produced by most pyelonephritic strains of Escherichia coli. P pili are assembled via a chaperone/usher pathway. Similar pathways are responsible for the assembly of over 30 adhesive organelles in various Gram-negative pathogens. P pilus biogenesis has been used as a model system to elucidate common themes in bacterial pathogenesis, namely, the protein folding, secretion, and assembly of virulence factors. The structural basis for pilus biogenesis is discussed as well as the function and consequences of microbial attachment.

Molecular cloning and characterization of Dr-II, a nonfimbrial adhesin-I-like adhesin isolated from gestational pyelonephritis-associated Escherichia coli that binds to decay-accelerating factor

Bacterial adhesins play an important role in the colonization of the human urogenital tract. Escherichia coli Dr family adhesins have been found to be frequently expressed in strains associated with pyelonephritis in pregnant females. The tissue receptor for known Dr adhesins has been localized to the short consensus repeat-3 (SCR-3) domain of decay accelerating factor (DAF), a complement regulatory protein. In this report, we identified and cloned draE2, a gene encoding a novel 17-kDa DAF-binding adhesin, Dr-II, from a strain of E. coli associated with acute gestational pyelonephritis. Despite the significant sequence diversity between Dr-II and Dr family adhesins, the receptor of Dr-II was found to be the SCR-3 domain of DAF. Sequence analysis of the 186-amino-acid Dr-II open reading frame revealed significant diversity from other members of the Dr adhesin family, including Dr, AFA-I, AFA-III, and F1845, but only an 8-amino-acid difference in sequence from that of the 17-kDa nonfimbrial adhesin NFA-I of unknown receptor specificity. N-terminal peptide sequencing of the purified adhesin confirmed the identity of the open reading frame and indicated cleavage of a 28-amino-acid signal peptide. Antibodies raised against purified Dr-II adhesin exhibited little or no cross-reactivity to Dr adhesin. Characterization of the biological properties demonstrated that like the Dr adhesins, Dr-II was associated with the ability of E. coli to bind to tubular basement membranes and Bowman's capsule and to be internalized into HeLa cells.

Distribution of drb genes coding for Dr binding adhesins among uropathogenic and fecal Escherichia coli isolates and identification of new subtypes

The Dr family of related adherence structures, some fimbriated and others afimbriated, bind to decay-accelerating factor molecules on human cells. Dr is associated with recurring urinary tract infection (UTI), but the distribution of Dr subtypes among uropathogenic Escherichia coli causing UTI among otherwise healthy women has yet to be described. A total of 787 UTI and fecal E. coli isolates from college women were screened for the presence of Dr sequences (drb). Fifteen percent of UTI strains were drb positive, compared to 5% of fecal strains. The adhesin (E gene) subtype of each drb-positive strain was determined by type-specific PCR followed by restriction enzyme analysis. Among 78 drb-positive strains, we found 14 (18%) afaE1, 1 (1.3%) afaE2, 1 (1.3%) afaE3, 9 (12%) draE, 9 (12%) draE-afaE3 hybrid, 1 (1.3%) daaE, 32 (41%) afaE5, 4 (5.1%) F131 E gene-like, and 7 untypeable strains. All untypeable E genes were cloned and sequenced, revealing four additional new classes of E genes, including two similar to the previously identified nonfimbrial E series. While a great range of diversity exists among the E genes, restriction fragment length polymorphism analysis demonstrated that all of these drb operons share a highly conserved gene structure. The most common subtype, afaE5, occurred three times as often among UTI than fecal strains. Over half of the drb-positive strains and 80% of those positive for afaE5 have the same virulence signature (positive for aer, kpsMT, ompT, and fim), suggesting an association of this profile with UTI pathogenesis.

Molecular basis of two subfamilies of immunoglobulin-like chaperones

The initial encounter of a microbial pathogen with the host often involves the recognition of host receptors by different kinds of bacterial adhesive organelles called pili, fimbriae, fibrillae or afimbrial adhesins. The development of over 26 of these architecturally diverse adhesive organelles in various Gram-negative pathogens depends on periplasmic chaperones that are comprised of two immunoglobulin-like domains. All of the chaperones possess a highly conserved sheet in domain 1 and a conserved interdomain hydrogen-bonding network. Chaperone-subunit complex formation depends on the anchoring of the carboxylate group of the subunit into the conserved crevice of the chaperone cleft and the subsequent positioning of the COOH terminus of subunits along the exposed edge of the conserved sheet of the chaperone. We discovered that the chaperones can be divided into two distinct subfamilies based upon conserved structural differences that occur in the conserved sheet. Interestingly, a subdivision of the chaperones based upon whether they assemble rod-like pili or non-pilus organelles that have an atypical morphology defines the same two subgroups. The molecular dissection of the two chaperone subfamilies and the adhesive fibers that they assemble has advanced our understanding of the development of virulence-associated organelles in pathogenic bacteria.

Structural and functional homology between periplasmic bacterial molecular chaperones and small heat shock proteins

The periplasmic Yersinia pestis molecular chaperone Caf1M belongs to a superfamily of bacterial proteins for one of which (PapD protein of Escherichia coli) the immunoglobulin-like fold was solved by X-ray analysis. The N-terminal domain of Caf1M was found to share a 20% amino acid sequence identity with an inclusion body-associated protein IbpB of Escherichia coli. One of the regions that was compared, was 32 amino acids long, and displayed more than 40% identity, probability of random coincidence was 1.2 x 10(-4). IbpB is involved in a superfamily of small heat shock proteins which fulfil the function of molecular chaperone. On the basis of the revealed homology, an immunoglobulin-like one-domain model of IbpB three-dimensional structure was designed which could be a prototype conformation of sHsp's. The structure suggested is in good agreement with the known experimental data obtained for different members of sHsp's superfamily.

Nucleotide sequences of two fimbrial major subunit genes, pmpA and ucaA, from canine-uropathogenic Proteus mirabilis strains

Proteus mirabilis strains were isolated from dogs with urinary tract infection (UTI) and fimbriae were prepared from two strains. The N-terminal amino acid sequences of the major fimbrial subunits were determined and both sequences appeared identical to the N-terminal amino acid sequence of a urinary cell adhesin (UCA) (Wray, S. K., Hull, S. I., Cook, R. G., Barrish, J. & Hull, R. A., 1986, Infect Immun 54, 43-49). The genes of two different major fimbrial subunits were cloned using oligonucleotide probes that were designed on the basis of the N-terminal UCA sequence. Nucleotide sequencing revealed the complete ucaA gene of 540 bp (from strain IVB247) encoding a polypeptide of 180 amino acids, including a 22 amino acid signal sequence peptide, and the pmpA (P. mirabilis P-like pili) gene of 549 bp (from strain IVB219) encoding a polypeptide of 183 amino acids, including a 23 amino acid signal sequence. Hybridization experiments gave clear indications of the presence of both kinds of fimbriae in many UTI-related canine P. mirabilis isolates. However, the presence of these fimbriae could not be demonstrated in P. vulgaris or other Proteus-related species. Database analysis of amino acid sequences of major subunit proteins revealed that the UcaA protein shares about 56% amino acid identity with the F17A and F111A major fimbrial subunits from bovine enterotoxigenic Escherichia coli. In turn, the PmpA protein more closely resembled the pyelonephritis-associated pili (Pap)-like major subunit protein from UTI-related E. coli. The evolutionary relationship of UcaA, PmpA and various other fimbrial subunit proteins is presented in a phylogenetic tree.

Modelling of steric structure of a periplasmic molecular chaperone Caf1M of Yersinia pestis, a prototype member of a subfamily with characteristic structural and functional features

Steric structure of Caf1M, a periplasmic molecular chaperone of Yersinia pestis, was reconstructed by computer modelling based on a statistically significant primary structure homology between Caf1M and PapD protein from Escherichia coli, and using the known atomic coordinates obtained by the X-ray crystallography for PapD. In the three-dimensional model of Caf1M an accessory sequence between F1 and G1 beta-strands (as compared to PapD) can form a strain-specific part of the binding pocket of surface organell subunits. This accessory sequence decreases the depth of the binding pocket. The characteristic structural feature of the subfamily of periplasmic molecular chaperones with the accessory sequence (Caf1M subfamily) is the existence of exposed to a solvent Cys residues in F1 and G1 beta-strands which can form disulfide bond in the putative binding pocket. The characteristic functional feature of Caf1M subfamily is the chaperoning of more simple compositions of virulence-associated surface organells (in the case of Y. pestis a capsule consists of only F1 protein). Highly conserved R82 and D93, located at the domain surface remote from the putative subunit binding pocket, can participate in direct contacts with the conserved portion of molecular usher proteins.

Nucleotide sequence of the afimbrial-adhesin-encoding afa-3 gene cluster and its translocation via flanking IS1 insertion sequences

The afa gene clusters encode afimbrial adhesins (AFAs) that are expressed by uropathogenic and diarrhea-associated Escherichia coli strains. The plasmid-borne afa-3 gene cluster is responsible for the biosynthesis of the AFA-III adhesin that belongs to the Dr family of hemagglutinins. Reported in this work is the nucleotide sequence of the 9.2-kb insert of the recombinant plasmid pILL61, which contains the afa-3 gene cluster cloned from a cystitis-associated E. coli strain (A30). The afa-3 gene cluster was shown to contain six open reading frames, designated afaA to afaF. It was organized in two divergent transcriptional units. Five of the six Afa products showed marked homologies with proteins encoded by previously described adhesion systems that allowed us to attribute to each of them a putative function in the biogenesis of the AFA-III adhesin. AfaE was identified as the structural adhesin product, whereas AfaB and AfaC were recognized as periplasmic chaperone and outer membrane anchor proteins, respectively. The AfaA and AfaF products were shown to be homologous to the PapI-PapB transcriptional regulatory proteins. No function could be attributed to the AfaD product, the gene of which was previously shown to be dispensable for the synthesis of a functional adhesin. Upstream of the afa-3 gene cluster, a 1.2-kb region was found to be 96% identical to the RepFIB sequence of one of the enterotoxigenic E. coli plasmids (P307), suggesting a common ancestor plasmid. This region contains an integrase-like gene (int). Sequence analysis revealed the presence of an IS1 element between the int gene and the afa-3 gene cluster. Two other IS1 elements were detected and located in the vicinity of the afa-3 gene cluster by hybridization experiments. The afa-3 gene cluster was therefore found to be flanked by two IS1 elements in direct orientation and two in opposite orientations. The afa-3 gene cluster, flanked by two directly oriented IS1 elements, was shown to translocate from a recombinant plasmid to the E. coli chromosome. This translocation event occurred via IS1-specific recombination mediated by a recA-independent mechanism.

Identification and characterization of a gene cluster mediating enteroaggregative Escherichia coli aggregative adherence fimbria I biogenesis

The aggregative pattern of adherence (AA) exhibited by enteroaggregative Escherichia coli upon HEp-2 cells is a plasmid-associated property which correlates with aggregative adherence fimbria I (AAF/I) expression and human erythrocyte hemagglutination. By using cloning and mutagenesis strategies, two noncontiguous plasmid segments (designated regions 1 and 2) required for AA expression have previously been identified in enteroaggregative E. coli 17-2. TnphoA mutagenesis was performed on clones containing region 1, and 16 TnphoA mutants which were negative for the AA phenotype were analyzed. The TnphoA insertion site for each mutant was determined by junctional DNA sequencing. All 16 mutations occurred within a 4.6-kb span in region 1. Nucleotide sequence analysis of the region revealed four contiguous open reading frames, designated aggDCBA, in the same span. AA-negative TnphoA insertions into all open reading frames except aggB were obtained. On the basis of mutational analysis and protein homology data, it is inferred that aggA, aggC, and aggD are involved in biogenesis of AAF/I, encoding a major fimbrial subunit, outer membrane usher, and periplasmic fimbrial chaperone, respectively. By immunogold electron microscopy, polyclonal antiserum raised against the aggA gene product decorated AAF/I fimbriae, affirming that AggA encodes an AAF/I subunit.